This invention relates generally to the finishing of stone, and is more particularly concerned with a polishing head that can be used for all stages of the polishing procedure, and for all kinds of stone. The usual stone polishing arrangement comprises a flat plate equipped with specialized restraining device that receive abrasive bricks. Such an arrangement is known as a Frankfurt plate and can successfully polish marble, sandstone and limestone.
To polish granite, specialized heads have been required, the head being quite complex. Such specialized heads are shown in the U.S. Pat. No. 4,965,965 to Wallin et al. and U.S. Pat. No. 5,151,331 to Zambon. In both these devices, it will be noted that the abrasives are carried by pivoted arms that rock. As a result, the abrasive wears to a rounded surface and makes only line contact with the stone being polished.
In general, granite is not homogenous but is made up of hard quartz crystals cemented together by a softer surrounding matrix. Known devices embody resiliently mounted abrasive plates which tend to tilt thereby causing the cutting element to touch the stone surface at the leading and trailing edges. This results in unwanted distortion of the surface of the stone. For instance, U.S. Pat. No. 2,717,478 to Blum and U.S. Pat. No. 2,860,496 to Tocci-Guilbert include grinding elements which could tilt and dig into the stone's surface.